What can we legally ask in screening a felon? (sex offender)

[Sarah Buchanan]

I had a potential tenant contact me and ask if I accept felons.  I have read that it's illegal (discrimination) to flat out say "no felons" so I asked what the crime was.  He said "sex offender, 16 years ago when I was 18 years old".  I told him I would "review with the owner" and get back to him.  Since then, I've been trying to read up on what I can legally ask him.  Can I ask him more details on his crime?  E.g. if it was consensual sex with a minor girlfriend 16 years ago, I don't feel I need to disqualify him if he's been clean for 16 years since (of course I'll do a background check to verify).  If it was violent or more serious in nature, I would disqualify him.  But I am wondering where I can learn/research more about what specific questions I can legally ask prospective tenants. Also - this is a single family, C property and there are 2 registered sex offenders in the apartments across the street so....I definitely still screen all tenants but have to have realistic standards for this type of a property.